Hi,
Its obvious that system would have determined the G/L and posted in the G/L account, otherwise system will not allow the user to post the transaction. Not sure why the Account is showing blank. In change layout, choose the column "G/L account" (there are two, check both) and see whether you are able to see the account. Also, check the General Ledger View of accounting entries.
Regards,
Sudeep.